Sound producer



March 17, 1959 J. w. KARSTED ETAL 2,877,862

SOUND PRODUCER Filed March 1; 1956 2 Sheets-Sheet 1 INVENTORS.

BY MM 3 M21 March 17, 1959 J. w. KARSTED ETAL 2,877,862

SOUND PRODUCER Filed March 1, 1956 2 Sheets-Sheet 2 Fig. 4

Fig. 7

Jessie W. Karsfed lrw'n F. Sumner INVENTORS.

BY W

United States Patent SOUND PRODUCER Jessie W. Karsted, Washington, D.C., and Irvin F. Sumner, Hyattsville, Md.

Application March 1, 1956, Serial No. 568,760

4 Claims. (Cl. 181-27) This invention relates to rotatable tremulantsound producers of the type in which the quality of musical productionis enhanced by producing a pitch tremolo or vibrato effect which is dueto a rotational movement of a sound transmitting channel.

The pitch tremolo or vibrato effect of this arrangement is not theresult of actual pitch variations, but is due to the rotational movementof a sound transmitting channel which, during its rotation, alternatelymoves towards and away from the listener, and thus causes variations inthe pitch of the tone received according to Dopplers principle.

While the pitch tremolo or vibrato effect based on Dopplers principleproduces a great improvement in the tone quality in the case of electricorgans, there is still much ditference between the playing of the samemusical selection on a pipe organ and on an electric organ. While thisdifference in tone quality, as well known, is of a most elusivecharacter and is only partly susceptible of being analyzed and measured;it is at least partly due to certain properties of the electrical soundproducing equipment and to the limitations imposed by the saidequipment, which limitations are only partly eliminated by the abovedescribed rotating tremulant sound producer.

Among the known causes of a deficient tone quality of the electric soundgenerator is the fact that every electric sound generator or speakercontains a membrane, usually a conical membrane which, to obtain maximumfidelity and to reduce distortion to a minimum, is as nearly aperiodicas possible. This aperiodicity not only eliminates distortion but alsothose oscillations which produce richness of tone. In a pipe organ, forinstance, the pipe sounds with a plurality of frequencies, with aplurality of harmonics and during the sounding of the pipes especiallywhen sounding chords, further frequencies are introduced by the pipeassembly. Further, the pipes, while arranged close to each other,nevertheless, sound from different places at different levels alllocated in a substantially horizontal zone and as the sound beam spreadsthey intermingle giving a so-called tout ensemble effect, which cannotbe reproduced by conventional electrical sound generators.

The rotatable tremulant speaker arrangement, like most high fidelitysound producers, is provided with two speakers one for the high andmedium frequencies (treble tones with frequencies between 4000 and 4500to 15,000 C. P. S.) and the other for the low frequencies (bass toneswith frequencies below 4000 C. P. 8.), each frequency range beingemitted through a separate, rotatable, tremolo producing transmissionchannel.

To produce the Doppler effect and to avoid one of the main disadvantagesof the electric sound reproducers, namely the so-called point sourceeffect, the sound emis sion for the treble tone speaker takes placethrough the top of the cabinet containing the speakers, and in additionthrough an opening in the side wall of the cabinet.

This is imperative as the transmission of sound through a side wallopening of the cabinet alone would produce a 2,877,862 Patented Mar. 17,1959 2 reception with pulsating intensity and would impair the Dopplereffect. Emission through two paths, one supplementing the other istherefore indispensable.

On account of the directive properties of high and medium frequencybeams the sound emitted through the top of the cabinet must be reflectedtoward the listener so that a most important part of the sound emissionis dependent on external reflecting surfaces, such as the ceiling andthe walls of the room in which the speaker arrangement is operated. Thehigh and medium frequencies which are emitted through ditferent openingsand in two directions and the low frequencies which are emitted at thelower end of the cabinet are thus solely combined by the fact that theyreach the listeners ear simultaneously from these three emissionsources.

The necessity of the sound emission through the top leads to a verticalsuperposition of the speakers which produces a cabinet structure ofundesirable height and unusual dimensions and proportions which makes itdifficult to introduce the cabinet into a home and especially to assignit to a place in those rooms of the home in which a speaker arrangementis actually used.

The invention has for its main object to correct some of the defectswhich are not corrected by the tremulant rotatable speaker arrangementor which are inherent in the same as now used. It has especially for itsobject to produce an improved tone quality and to re-introduce some ofthe effects which the known tremulant double speaker arrangement haseliminated.

Further the invention has for its object to provide a tremulant speakerarrangement which may be housed in a cabinet of chest-like appearancewhich has the look and the proportions of a well designed piece offurniture thus making it possible to introduce a speaker arrangementinto homes and to place it in those rooms of a home in which they areactually used, as a piece of furniture fitting the remainder of thefurniture.

The improvement of the tone quality is essentially produced byconducting that portion of the sound which, in the known tremulantspeaker arrangement, is emitted through the top, through a substantiallyhorizontal transmission compartment or intercornpartment channelconnecting the treble speaker compartment with the bass speakercompartment into the latter and emitting it from said compartment. Thesubstantially horizontal intermediary intercompartment channel adds tothe passing sound certain reverberation effects, while conducting it tothe bass speaker compartment from which high frequencies and lowfrequencies are now simultaneously emitted.

The portion of the sound which is conducted to the low speakercompartment is supplemented by the direct sound emission through anopening in the compartment of the treble speaker.

The method of emitting a major portion of the high and mediumfrequencies from the compartment from which also the low frequencies areemitted, after their passage through the intercompartment reverberationchannel introduces not only the desired amount of reverberation, whichmay be regulated by a proper design of the channel, but also permits touse the speaker arrangement for instruments other than organs; itfurther produces a complete mingling of the frequencies before theyreach the listeners ear which together with the horizontal spreading ofthe sound emission due to the horizontal alignment of the sound emissionsources produces an effect which is very similar to the tout ensembleeffect of the pipe organ.

The insertion of the intercompartment channel by introducing a desiredreverberation effect eliminates a well known disadvantage of theelectric speaker arrangement which consists in the instantaneous settingin of every tone, a property which has often been criticized especiallyin connection with electric organs and harmoniums. The above describedarrangement by virtue of the combined wayof emitting the higherfrequencies using two different emission channels eliminates thisinstantaneous response and thus produces a tone quality which is moreassimilated to that of a non-electric instrument.

The attenuation of the higher frequencies due to refiection iscompensated by the direct emission of the high frequencies through anopening in the cabinet which in a horizontal arrangement may be beameddirectly towards the listener, seated at a convenient distance, ratherthan being beamed into space above the listeners head, as is the casewith the known tremulant speakers in which the top of the cabinet mustbe located at a considerable height with the rotatable horn directedupwardly, thus necessitating beaming through the opening of the cabinetat a relatively high level.

A number of further objects of the invention and a number of furtheradvantages will be apparent from the following detailed specification.

The invention is illustrated in the accompanying drawings showing oneembodiment thereof by Way of example. It is however to be understoodthat the embodiment of the invention illustrated in the drawings isshown by way of example only with a view of explaining the principle ofthe invention and the best mode of carrying the principle into effect.It will be clear to the expert skilled in this art that modifications ofthe invention introduced to adapt the invention for various instrumentsmay be introduced Without in any way departing from the principle of:the invention.

In the drawings:

Figure 1 is aperspective view of a tremulant sound producer unitaccording to the invention, the cabinet having the shape of a low chestprovided with several doors.

Figure 2 is an elevational rear view of the cabinet.

Figure 3 is an elevational partly sectional view of the unit with thedoors, front wall and textile covering in front removed, the partitionwalls being partly shown in section.

Figure 4 is an elevational sectional view of the unit, the section beingtaken along line 4-4 of Figure 3.

Figure 5 is an elevational sectional View of the unit, the section beingtaken along line 55 in Figure 3.

Figure 6 is an elevational sectional view of the low frequency speakercompartment, the section being taken along line 66 in Figure 3.

Figure 7 is a perspective view of the unit according to the prior art.

To produce by means of an electromagnetic sound generator a tonalquality which is closer to that of tones produced in pipe organs thespeaker assembly illustrated in Figure 7 has been developed. Thisarrangement forms part of the known art and has been described in patentRe. No. 23,323 to Leslie. It is based on the principle of reproducingthe higher and medium frequencies on one hand (treble tones) and belower frequencies (bass tones) by means of different electromagneticspeakers to obtain a higher fidelity; in addition a pitch tremolo orvibrato of each tone is produced by associating the stationary part ofeach speaker with a rotating sound transmitting channel, the mouth ofwhich is arranged at a distance from the axis of rotation.

As seen in Figure 7 which represents such a prior art arrangement acabinet 61 contains in its uppermost portion a compartment 64 containinga treble speaker 62, the stationary part of which, including a membraneand voice coil, emits sounds which are collected by an exponential horn63 which is rotatably arranged and turns around an axis which iscoincident with the axis of the speaker membrane. The mouthpiece 65 ofthe exponential horn is arranged at a distance from the axis of rotationand it therefore moves at a predetermined circumferential speed. Thehorn is suitably mounted on a table with its inner or entrance endfacing the membrane of the speaker; it is journaled in bearings on saidtable and is preferably driven at a speed of 300 to 450 R. P. M. bymeans of an electric motor 66 and a belt drive.

It will be noted that the axis of the treble speaker is vertical andthat the exponential horn which forms the rotatable sound transmissionchannel is upwardly directed.

The bass speaker 74) is mounted in the lowermost compartment 73 of thecabinet 61 which carries a sound emitting horn '72 of a constant crosssection which is rotatably mounted on the sound board. This horn alsorotates around a vertical axis; it is driven by a separate motor 75 anda belt drive.

The cabinet 61 has a sound opening 77 at the top and a further soundopening (not shown) in the front wall at the level of the mouth 65 ofthe exponential horn of the treble speaker. Further, sound openings areprovided at the bottom of the cabinet at the level of the zone ofmovement of the mouth of the rotating horn 72 of the bass speaker, oneof said openings being shown at 78.

Such a speaker arrangement in order to be effective must be arranged inthe manner illustrated showing a vertical super-position of the speakerswith the treble speaker arranged on the top. This arrangement isnecessary for several reasons one of them being that the sound producedin the treble speaker must escape through the top of the cabinet, inorder to provide continuous sound emission with the intended pitchvariation, resulting in a pitch tremolo or vibrato produced by theDoppler eifect which is due to the movement of the mouth of the horn.Such vibrato or tremolo would not result if the moving horn would solelyemit sounds through a lateral opening of the cabinet as the high andmedium frequencies on account of this directional characteristic wouldbe beamed at the listener only during the passage of the mouth of thehorn behind the lateral opening. The pitch tremolo or vibrato would beattenuated while the intensity variations would be very marked.

To emit the sound through the top an upwardly directed exponential hornmust be used and the sound beam must be reflected on the side walls ofthe cabinet compartment 64. The advantage of this arrangement consistsin distributing the sound emission over a considerable area, thusavoiding the detrimental influence on the tone known as a single pointsource effect. The main advantage of the arrangement is, however, toproduce the Doppler effect which varies the pitch without submerging itbeneath considerable intensity variations of the sound. However, thistype of sound emission also is accompanied by some disadvantages, as theemitted sound is attenuated and must be emitted upwardly at a highlevel. It reaches the listener partly by reflection from the ceiling andthe side walls of the room in which the speaker arrangement is located,and the tone quality is thus partly governed by the height of theceiling, the proximity of other walls and other external circumstances.Further, the dimensions are necessarily such that the speaker assemblycabinet forms a piece of furniture of objectionable height, size andproportions as it must be relatively narrow and high and does not fitinto customary furniture proportions.

The bass speaker is necessarily close to the floor in this case andwhile low frequency beams expand easily the listener has to combinesound waves arriving from three directions: the sound waves emitted bythe bass speaker coming from below, the sound waves beamed directlythrough the opening in the cabinet, and the high frequency sound Waveswhich reach the listener by reflection from the ceiling and the sidewalls of the room.

Now the division of frequencies between upper and lower speakers isarbitrary from the standpoint of the listener, as it does not follow anymusical principle, but

is due to the somewhat variable capability of the speaker membrane toreproduce sound with fidelity. The line is usually drawn at frequenciesof about 4000 to 4500 C. P. S. the frequencies ranging from 4000 to15,000 C. P. S. being emitted through the high frequency speaker.Speech, vocal music and many instruments produce however sounds whichfall in both ranges, thus producing for the listener the somewhatstartling effect of hearing the same voice or instrument from differentdirections. On account of this the arrangement is limited to electricorgans where this distribution is not as disturbing as in otherinstruments, but even in organs the lower frequencies are separated fromtheir harmonics and the mingling of the sound is imperfect so that theso-called tout ensemble" effect is lost.

By means of the invention some major causes for the difference in theperformance between the electric sound producer and the original musicalinstrument are eliminated and a higher tone quality is obtained.Further, the limitation of the rotary arrangement to an electric organisno longer necessary and other music can be produced with good quality.

According to the invention the compartments containing the two rotatingsound transmission channels are no longer completely independent soundemitting units, emitting sounds separately, but are joined by anintercompartment transmission channel shaped and arranged to form anacoutically active intermediate reverberation compartment which has themultiple function of transmitting that part of the higher frequencies,which, in the known arrangement, is emitted through the top, to the lowfrequency compartment and of producing a desired amount of reverberationby reflection within the cabinet. Thus a complete intermingling orblending of high and low frequencies coupled with a reverberation effectwithin the cabinet is produced which greatly improves the tone' qualityand makes it independent of the surroundings.

The principle of using, in addition to the transmission of the high andmedium frequencies through the intermediary compartment to the lowfrequency compartment, the direct beaming of high and medium frequenciestoward the listener by means of an opening in the high frequencycompartment is however retained. The arrangement of an intermediaryreverberation compartment and the emission of part of the high andmedium frequencies through the low frequency compartment makes avertical arrangement unnecessary and permits a horizontal arrangement.This horizontal arrangement in the first place is an improvement insofaras the production of music by means of tones all generated along ahorizontal plane or along a substantially horizontal zone is the ruleand is something to which the listener is accustomed, as mostinstruments (piano, organ, harmonium and all orchestras) show ahorizontal spacing of the tone producing sources.

In addition to this material improvement of the tone effects thearrangement also permits a radical change in the outward appearance ofthe cabinet making it possible to design a cabinet in the shape of a lowchest. This is a major advantage as such a design permits the use of thecabinet within a home without producing an incongruous effect, such asis necessarily produced by a cabinet with a vertical superposition ofthe speakers which almost invariably has unusual proportions,conspicuously differing from known furniture proportions and whichtherefore does not harmonize with existing furniture. Further thegeneral utility of a low chest within a home is unquestionable, whilenot much use can be found in a vertical structure.

As seen in Figure 1 the unit according to the invention comprises acabinet 11 having the approximate proportions of a low chest with topand bottom walls 19 and 29 and side walls 26 which may be permanentlyjoined to each other. A rear wall 47 (Figure 2) which may be made of onepiece, but which preferably consists of several pieces, is attached byscrews 49 which can be removed for the purpose of mounting, dismountingand repairing the various units arranged in the interior. If the rearwall is subdivided it preferably consists of three parts, each coveringone of the compartments to be described below.

The front of the cabinet may be completely covered by a textile fabric50, irrespective of whether or not a sound emitting or a non-emittingcompartment is arranged behind it, in order to produce a unitary andpleasing appearance of the front. In order to improve the impression ofan attractive piece of furniture the cabinet may be provided with doors37, 29, 37a, 39a which may be closed when the instrument is not in useand which are opened in the manner shown in Figure 1 during the use ofthe speaker arrangement. In this position of the doors all the soundemitting compartments are uncovered.

The cabinet 11 is divided into compartments, two of these compartmentsbeing speaker compartments 10, 12 which are arranged near the two endsof the cabinet. These two speaker compartments are joined by a soundtransmitting intercompartment channel 15 in the shape of an intermediarycompartment which also forms a reverberation chamber.

The compartment 10 houses a speaker 20 emitting the high and mediumfrequencies, usually the range of frequencies above 4000 to 4500 C. P.S., which speaker is mounted on a sound bafiie or sound board 14arranged in the upper part of the compartment 10. This baffle or soundboard 14 acts as a support for the rotating sound emission assembly 20and forms a partition, so that the speaker assembly 20 is enclosedwithin a subcompartment 17 of the compartment 10. The speaker assemblycorresponds essentially to that described in connection with the knownunit already described in connection with Figure 7 although thearrangement of parts in detail may somewhat differ. The speaker ispreferably fixedly carried by the sound board 14 itself and the voicecoil of the speaker is driven by an amplifier 18 which may be arrangedin the lower subcompartment of the compartment 10. The amplifier isshown to be connected by means of a cable 23 with the console of amusical instrument (for instance, an organ) of which the sound producerforms a part.

As well known the oscillating currents into which the sound oscillationshave been translated must be divided and distributed between the twospeakers according to their frequency and this distribution of thefrequencies between the treble and bass speakers is performed by aso-called dividing network 38 which may be arranged in the lowersubcompartment of the compartment 10 or may be mounted on the partitionwall 22 separating the compartment 10 from the intermediate compartment15.

The speaker 16 is a treble speaker and is provided with a membranearranged in front of the exponential directional horn 25 which isrotatably supported on a horn support 21 resiliently mounted on thebaseboard 14. The rotatable support 21 is provided with a pulley 27driven by means of a belt drive 28 by an electric motor 30. The rotatingexponential horn preferably forms part of a symmetrical structure, onlyone side of which contains an exponential channel. The mouth of theexponential horn must be located at a distance from the axis ofrotation.

The upwardly directed inclination of the exponential horn is lesspronounced than the inclination of the horn according to the knownarrangement. This is due to the fact that in the known arrangement thehorn is supposed to emit sound against the wall of the compartment inwhich the speaker is enclosed from which wall the beam is reflectedtowards the top. The marked upward inclination of the exponential horn,required in the known arrangement, is however a disadvantage inconnection with the transmission of the treble tones through the soundopening provided in the compartment. A high frequency sound beam isdecidedly directional and this still holds good for the mediumfrequencies. The exponential horn accentuates the directional effect andtherefore the treble frequencies are beamed through the opening over thehead of the listener and reach the listener only after reflection on theceiling and on the Walls of the room in which the speaker assembly isoperated. The proper intermingling of the treble frequencies with thebass frequencies which are emitted from another point is thereforelargely dependent on the room in which the instrument is played and onthe location of theinstrument within the room.

In the improved arrangement according to the invention the emission'atthe top of the cabinet is eliminated and the treble speaker emits itssound mainly into the intermediary compartment 15. This is done by meansof a large elongated opening 32 which is provided in the wall 22separating the treble speaker compartment 10 from the said intermediarycompartment 15.

The specific arrangement may be such that in the position illustrated inFigure 3 the mouth of the exponential horn enters said opening in theintermediary compartment 15 while during other phases of the rotationalmovement of the exponential horn the sound enters the compartment afterreflection from the walls of the treble speaker cm partment 10.

Further, the front of the treble speaker compartment is open or may beprovided with an opening 31 through which the sound is emitted directlytowards the listener. The exponential horn Z5 is somewhat upwardlyinclined, while the treble speaker compartment is normally arrangedbelow the level of the listeners ear. The beam emitted by theexponential horn of the treble speaker emitted in an upwardly inclineddirection may thus reach the ear of the listener directly during thatphase of the rotation during which the exponential horn is pointedtowards the front and will thus supplement the treble frequencies whichreach the listener after reflection.

The intermediary compartment is of suitable size and is completelyclosed or surrounded by walls on all sides, the side walls 22, 34,leading to the compartments l0 and 12 of the speakers, being providedwith openings or perforations 32, 33. The side wall .22 is preferablyprovided with one large opening 32 while the other wall 34 is providedwith series of openings 33 leading to the low frequency or bass speakercompartment 12.

The wall 34 separating the intermediary sound transmission channel 15from the bass speaker compartment 12 may be used as a baffle or soundboard for the bass speaker 36 which may be centrally arranged withrespect to this wall in such a manner that its frame projects into theintermediary compartment 15. In front of the membrane of the bassspeaker 36 a rotary transmission channel 40 is provided which is similarto the one already described in connection with the prior art but whichin this case is mounted horizontally. It is rotated around thehorizontal axis 42 which carries the pulley 41 driven by a smallelectric motor 4 by means of a belt drive 43. The motor 44 may bemounted on the bottom wall of the compartment 12. The horizontalarrangement of the axis of rotation has the great advantage that onaccount of the vertical position of the axis of rotation of the assemblyvibrations due to mechanical influences are not likely to occur, thusexcluding a troublesome source of disturbances.

The front of the bass speaker compartment 12 is completely or partlyopen. It may be provided with the customary louvers or grill. As alreadymentioned, the open portions of both speaker compartments l0 and 12 maybe covered by a textile fabric 50 which also covers, for the sake ofbetter appearance, the closed wall of the intermediary intercompartmenttransmission channel.

In operation it will be clear that the frequencies com- .ing from theelectric organ are divided into treble and 8 bass frequencies by thedividing network, the former being supplied to the treble speaker 20.The sound produced by the treble speaker partly is transmitted throughthe opening 32 and partly through the front opening 31 of the treblespeaker compartment. The vibrato or tremolo effect due to the rotationof the transmitting exponential channel remain essentially unchanged.However, the sound emitted, penetrates into the intermediary compartmentor intercompartment transmission channel 15 through the elongatedopening 32. This intermediary compartment orintercompartmenttransmission channel 15 produces a certain amount of reverberation whichis highly desirable to improve the tone quality and which can be sochosen that the optimal tone qualityis obtained. As seen this tonequality is independent of the surroundings. From the intercompartmenttransmission channel 15 the sound penetrates into the compartment 12 ofthe bass speaker through the openings 33 and is emitted through the bassspeaker compartment opening simultaneously with the lower frequenciescoming from the bass speaker. The high frequencies and the lowfrequencies are therefore mingled and blended and the resulting tone isthus felt by the listeners to be of a much better quality than a tonebeamed from two different places which becomes a composite frequencytone merely in the listeners ear. Also, the necessary amount ofreverberation is imparted to it without affecting the desired tremolo orvibrato effect which is practically unchanged. This arrangement thuslargely eliminates the majority of the defects of the electric soundgenerator.

The invention thus produces a number of advantages relating to thegreater assimilation of the quality of the musical sounds produced tothe known manually operated musical instrument, and further relating tothe reduction of disturbances, as well as to the shape, the generalesthetic qualities and the utility of the cabinet.

It will be clear that unessential changes may be made without in any waydeparting from the principle of the invention as defined in the annexedclaims.

What is claimed as new is as follows:

1. A cabinet for electrically operated musical instruments comprising aplurality of horizontally aligned compartments, a sound generatorproducing sounds of the upper frequency range in the first one of thesaid compartments, a sound generator producing sounds of a lowerfrequency range in a second one of said compartments, said first andsaid second compartment being arranged at a horizontal distance fromeach other, a third one of said compartments between said first and saidsecond compartment, forming an intermediate reverberation producingsound transmitting channel, aligned passages leading from the first intothe intermediate compartment, and from the intermediate compartment intothe second compartment respectively, each of the sound generator housingcompartments being provided with sound outlets leading to the outside,the sound generator producing sounds of the upper frequency rangeincluding a rotating horn having a sound orifice sweeping duringrotation past the outlet opening in the first compartment leading to theoutside and the passage leading to the intermediate compartment, thesounds of the upper frequency range being thus alternatively emittedthrough the outlet opening in the first compartment and transmittedthrough the aligned passages of the reverberation producing intermediatecompartment into the second compartment, from whence they are emittedthrough the outlet opening of said second compartment.

2. In a music producing apparatus with a plurality of electric soundgenerators, each operating within a definite frequency range, thegenerator emitting higher frequencies being provided with a horn havinga sound emitting orifice, rotating at apredeterinined speed about anaxis transverse to the horn axis: a cabinet with a plurality ofseparate, spaced sound generator compartments, each provided with asound outlet opening, said compartments being joined by an intermediatecompartment forming a sound channel producing a predetermined amount ofreverberation during sound transmission, and means for emittingalternatively with varying sound intensity through said outlets of saidseparate spaced sound compartments the high frequency sounds produced bythe high frequency generator and emitted through the rotating horn, saidmeans including aligned passages between the high frequency soundproducer compartment and the intermediate compartment and between thelatter and a second one of the plurality of spaced separate soundgenerator compartments, the first named of said aligned passages beingalso aligned with the annular zone along which the sound emittingorifice of the rotating horn moves during rotation, the high frequencysound thus reaching the listener alternatively and with varyingintensity through the outlet openings of the two sound generatorcompartments located at a distance.

3. A music producing apparatus with a plurality of electric soundgenerators, each operating within a definite frequency range, the soundgenerator emitting sounds of higher frequency being provided with a hornhaving a sound emitting opening rotating at a predetermined speed aboutan axis transverse to the horn axis, comprising an elongated cabinethaving a plurality of longitudinally spaced sound generatorcompartments, each compart ment housing one of the electric soundgenerators, an intermediate compartment between the sound generatorcompartments, said intermediate compartment forming a sound transmissionchannel producing a predetermined reverberation during soundtransmission, the compartment housing the generator emitting sounds ofhigher frequency being closed at the top and being essentially providedwith two emission openings arranged to be successively faced by thesound emitting opening of the rotating horn during rotation, one of theaforesaid two sound emission openings being an outlet opening leading tothe outside and the other opening leading to the intermediatecompartment, positioned so as to provide a straight passage of the soundemitted by the rotating horn into and through the intermediatecompartment, said last-named compartment being provided with a furtheropening, aligned with said straight sound passage and leading to thesound generator compartment housing the low frequency sound producinggenerator, the latter compartment being further provided with an outletopening, the high frequency sound leaving the rotating horn being thusemitted from the cabinet through the longitudinally spaced outletopenings with periodically increasing and decreasing intensity, theincrease and decrease of the intensity of the sound emitted through thelongitudinally spaced openings occurring at difierent times.

4. The musical sound producer as claimed in claim 3, wherein the soundgenerator producing sounds in the lower sound frequency range isprovided with a rotating horn, the axis of rotation of which is at rightangles to the axis of rotation of the horn of the sound generatorproducing sounds in the higher frequency range, the high frequencysounds entering the compartment housing the sound generator producingsounds in the lower frequency range passing said compartment insubstantial parallelism to the axis of rotation of the horn in saidcompartment.

References Cited in the file of this patent UNITED STATES PATENTS Re.23,323 Lesiie Jan. 9, 1951 1,712,516 Norris May 14, 1929 1,915,954Scofield June 27, 1933 2,224,919 Olson Dec. 17, 1940

